The present invention relates to a rocker arm made of sheet metal which is manufactured by a press work from a metal plate, out of rocker arms incorporated in a valve driving mechanism of an engine for converting a rotation of a cam shaft to a reciprocating motion of a valve unit (including a suction valve and an exhaust valve), as well as an improvement in a manufacturing method thereof.
The present invention also relates to a cam follower provided with a sheet metal rocker arm and an improvement in an assembling method thereof.
A reciprocating engine (reciprocating piston engine) is provided with a suction valve and an exhaust valve which opens and closes in synchronism with a rotation of a crank shaft, except a two-cycle engine provided in certain types. In such a reciprocating engine, a motion of a cam shaft which rotates in synchronism with a rotation of the crank shaft (at a rotation speed of xc2xd in case of a four-cycle engine) is transmitted to the intake valve and the exhaust valve by use of a rocker arm, and the intake valve and the exhaust valve are reciprocated along the axial direction.
Conventionally, such a rocker arm incorporated in the valve driving mechanism of the engine is generally formed by casting (as a cast iron or aluminum die cast product). However, a cast product is too weighty (in case of an iron cast) or bulky (in case of an aluminum die cast) for maintaining a sufficient strength. In addition, since the rocker arm is generally manufactured by a lost wax method, the manufacturing cost is unavoidably increased. For this reason, it is recently considered to manufacture such rocker arm by a press work from a metal plate such as a steel plate, which is partially realized.
A conventional manufacturing method of a sheet metal rocker arm considering such circumstances is disclosed in, for example, Japanese Patent Application Laid-Open No. 3-172506. FIGS. 19 to 22 show the manufacturing method of a sheet metal rocker arm disclosed in this application. According to this conventional method, first a metal plate (such as a carbon steel plate having the thickness of 2 to 4 mm) as blank is punched by the press work, so as to form a blank 1 having a shape as shown in FIG. 19A and the thickness of t1, as shown in FIG. 19B.
Next, this blank 1 is subjected to a bending work by press to form a first intermediate blank 2 as shown in FIGS. 20A and 20B. This first intermediate material 2 comprises a pair of side walls 3, 3 parallel to each other, a connecting portion 4 for connecting the edges of the both side walls 3, 3 in the width direction, a roller receiving recess 5 formed in a middle part of a space surrounded in three directions by the both side walls 3, 3, and the connecting portion 4, and a pivot portion 6 as a spherical concave surface formed in a middle part at a position nearer one end of the connecting portion 4.
Subsequently, a through hole 7 which has a Japanese hand drum shape when seen from the side parallel to the side walls 3, 3, as shown in FIGS. 21A and 21B, is formed in a portion which is a part of the connecting portion 4 for forming the first intermediate blank 2 as described above and is corresponding to the roller receiving recess 5, as a second intermediate blank 8. Arched protrusions 9, 9 which are part of the second intermediate blank 8 are provided to sandwich this through hole 7 from the both sides thereof in the width direction (the up-and-down direction in FIG. 21A) in a state that the protruding edges of both of the protrusions 9, 9 are placed opposite to each other. The through hole 7 has a narrower width W7 at the center thereof, compared with the width at a part nearer either of the ends thereof.
When a part surrounding the though hole 7 of the second intermediate blank 8 as described above is subjected to burring and ironing, a third intermediate blank 10 as shown in FIG. 22 is obtained. In this third intermediate blank 10, the through hole 7 becomes an opening 11 which has a rectangular shape when seen from the side parallel to the side walls 3, 3, and the shape of the other end portion of the connecting portion 4 is adjusted to become a valve engagement portion 12 for abutting on the base end portion of the valve unit constituting the suction valve or the exhaust valve. At the subsequent step, in the third intermediate blank 10 as described above, circular holes for supporting the both ends of a support shaft for supporting to allow free rotation a roller which is engaged with the cam are formed at positions aligned with each other on both of the side walls 3, 3, thereby completing a sheet metal rocker arm. Then, in a state that such sheet metal rocker arm is assembled in the engine, the outer peripheral surface of the roller which is supported by the roller receiving portion 5 in a rotating manner is brought into contact with the outer peripheral surface of the cam, the leading end portion of a lash adjuster is caused to abut upon the pivot portion 6, and the base end surface of the suction valve or the exhaust valve is caused to abut upon the valve engagement portion 12.
The thickness t3 of each of the laterally paired side walls 3, 3 for constituting the sheet metal rocker arm manufactured in the manner described above is substantially equal to the thickness t1 of the blank 1 (FIG. 19B) (t3_t1). The thickness t3 of each of the both side walls 3, 3 and the thickness t4 of the connecting portion 4 including the pivot portion 6 and the valve engagement portion 12 (FIG. 22B) are also substantially equal to the thickness t1 of the blank 1 (t1_t3_t4).
More specifically, since formed of one metal plate in a unitary structure mainly by the press work, the conventional sheet metal rocker arm mentioned above has substantially a uniform thickness over the entire surface thereof except a part of the pivot portion 6 and a part followed by a part of the metal plate. Also, in case of a conventional technology other than Japanese Patent Application Laid-Open No. 3-172506 mentioned above, a sheet metal rocker arm which is formed of one metal plate in a unitary structure mainly by the press work has substantially a uniform thickness over the entire surface thereof.
On the other hand, there is conventionally known a structure of a rocker arm in which two or three members respectively formed by the press work of a metal plate are connected and fixed to each other by welding. In case of a sheet metal rocker arm which is formed by combining plural members as stated, the thickness of the connecting portion including the pivot portion and the valve engagement portion is formed greater than the thickness of each of the side walls.
According to the conventional technology described above, inconveniences as stated below will be brought about. First, according to the technology disclosed in Japanese Patent Application Laid-Open No. 3-172506 for forming a sheet metal rocker arm from one metal plate in a unitary structure, the thickness of the formed sheet metal rocker arm is uniform substantially over the entire surface thereof. On the other hand, when the rocker arm is in use, a stress acting on the connecting portion 4, specially that acting in the vicinity of the valve engagement portion 12, is greater, compared with that stress acting on another portion such as the side walls 3, 3. For this reason, when the thickness is uniform, the connecting portion 4, specially in the vicinity of the valve engagement portion 12, is disadvantageous in terms of the strength, compared with other portions, and the rigidity also may be lowered in some cases. In case of the conventional technology, the thickness of the metal plate for forming the sheet metal rocker arm is made to be great in order to secure a sufficient strength and rigidity of a portion in the vicinity of the valve engagement portion 12. Consequently, the thickness of the other portions such as the side walls 3, 3 is greater than that originally required, so that the size and the weight of the sheet metal rocker arm can not be sufficiently reduced. In addition, the cost of materials is increased.
In case of the sheet metal rocker arm in which two or three members respectively formed of a metal plate by the press work are connected and fixed to each other by welding, the thickness of the connecting portion including the valve engagement portion can be made greater than the thickness of another portion such as the side wall. On the other hand, however, after plural members are formed separately, these members are required to be combined with each other and bonded together by welding. Consequently, the number of processing steps increases and an extra labor is required for controlling the constituent parts. Since a complicated and precise equipment is required for positioning the respective members when they are assembled, it is unavoidable to increase the cost, as well as to increase the number of processing steps and to require an extra labor for controlling the parts. Moreover, the quality of the obtained sheet metal rocker arm (precision) is often inferior to that of the rocker arm formed in a unitary structure.
Though having a superior toughness to the cast-type rocker arm, the sheet metal rocker arm may be elastically deformed more easily depending on a direction of action of the force. That is, since each of the paired walls 3, 3 for bridging the both ends of a pivot for supporting the roller takes a flat-plate shape, if a force in a right-angled direction is applied on the side walls 3, 3, the side walls 3, 3 are elastically deformed comparatively easily. On the other hand, when the both ends of the pivot is caulked toward the inner peripheral surfaces of both of the through holes for connecting and fixing the both ends of the pivot to each other, a force is applied onto portions which are provided on the side walls 3, 3 with the through holes formed thereon in a direction in which the both portions come toward each other. Then, the side walls 3, 3 are elastically deformed on the basis of this force.
In case of the conventional sheet metal rocker arm, the paired side walls 3, 3 are formed to be parallel to each other in a state prior to that the both ends of the pivot are caulked. For this reason, in a state in which the both ends of the pivot are caulked toward the inner peripheral surfaces of the through holes, the paired side walls 3, 3 are formed to be non-parallel to each other. Accordingly, the inner side surfaces (the side surfaces opposite to each other) of the side walls 3, 3 and the both end surfaces in the axial direction of the roller supported in a middle part of the pivot in a rotating manner are formed to be non-parallel to each other. As a result, the so-called edge abutment is brought about in which the inner side surfaces of the side walls 3, 3 and the both end surfaces of the roller in the axial direction are not brought into contact with each other in a uniformly wide area, but may be brought into contact with each other in a very narrow area, or the edges of the side walls 3, 3 and the both end surfaces of the roller in the axial direction are brought into contact with each other.
In such a state, it is difficult to satisfactorily form between the inner side surfaces of the side walls 3, 3 and the respective both end surfaces of the roller in the axial direction an oil film for decreasing a friction between these both surfaces. This is not preferable since a resistance required for a rotation of the roller may be increased, or an amount of abrasion of the roller or the sheet metal rocker arm may be increased.
When the cam follower with the sheet metal rocker arm is in use, the roller is rotated inside the roller receiving recess 5, which is provided on this sheet metal rocker arm. When this roller is displaced in the axial direction with respect to the pivot which is supported on and fixed to the sheet metal rocker arm, the end surface of the roller in the axial direction and the inner side surface of one of the side walls 3 rub against each other. Accordingly, it is required to decrease a frictional resistance of a contact portion between these end surfaces of the roller in the axial direction and the inner side surfaces of the side walls 3, 3 for reducing a rotational resistance of the roller and for reducing abrasion of this roller and the sheet metal rocker arm.
However, in case of the cam follower provided with the conventional sheet metal rocker arm, such requirements are not always taken into consideration.
A sheet metal rocker arm according to the present invention and a method of such rocker arm have been conceived to solve any of the above-described inconveniences.
According to the present invention, there is provided a sheet metal rocker arm manufactured by the steps of punching one metal material to form a blank having a predetermined contour and through holes, and subjecting this blank to a bending work based on a press work to form a pair of side walls parallel to each other and a connecting portion for connecting the both ends of the both side walls in the width direction thereof. This rocker arm is also provided with at least a pair of though holes formed at positions which are aligned with each other on the both side walls and at least one engagement portion provided in a part of the connecting portion. The thickness of the part in which at least one engagement portion is provided, out of this connecting portion, is formed to be greater than the thickness of the both side walls by increasing the thickness of the part in which at least one engagement portion is provided, out of this connecting portion, by the press work.
According to the method of manufacturing a sheet metal rocker arm of the present invention, when the sheet metal rocker arm as described above is manufactured, the blank is subjected to the bending to form both of the side walls, and a portion corresponding to the connecting portion is curved to have an arched section, thereby forming the curved portion. Then, a pressing work is conducted to strongly press this curved portion to be plastically deformed. Thus, the thickness of this curved portion is increased and an engagement portion is formed in this curved portion.
According to the sheet metal rocker arm of the present invention having the above-mentioned structure and the manufacturing method of such rocker arm, though the rocker arm is formed from one metal plate in a unitary structure having the uniform thickness, the thickness of the connecting portion including the valve engagement portion can be made greater than the thickness of the paired side walls. Consequently, it is possible to reduce a stress acting on the connecting portion including this valve engagement portion to secure a strength and a rigidity of the sheet metal rocker arm without unnecessarily increasing the weight of the rocker arm. It is suffice if the thickness of the side walls is great enough to secure the strength and the rigidity required for these side walls, and the thickness is not required unnecessarily great. Thus, it is possible to reduce the width of the sheet metal rocker arm, which is a distance between the outer side surfaces of the both side walls, so that a design incorporating this sheet metal rocker arm into a limited space inside the engine becomes easier.
Moreover, since the whole sheet metal rocker arm is formed from one metal plate in a unitary integral structure, an extra labor for connecting plural members separately manufactured is not necessary, thereby decreasing the number of the processing steps and preventing an increase in manufacturing cost as well as deterioration in precision. In addition, it is possible to save a complicated mechanism for assembly and positioning, so as to manufacture a sheet metal rocker arm with a high quality at a low cost. Further, it is possible to carry out a work for increasing the thickness of the connecting portion only by the press work without introducing a special equipment. For this reason, it is possible to suppress investment in equipment and to realize a sheet metal rocker arm with a high quality at a low cost by saving a labor with automated manufacturing steps.
The present invention has been contrived to further reduce the size and the weight of the sheet metal rocker arm. More specifically, when the sheet metal rocker arm is used, a stress is generated in each part based on a load applied from the valve unit and the lash adjuster. Unless the shape and the size of each constituent part are selected in relation with this load, the magnitude of this stress is in the respective parts. Naturally, in order to secure a sufficient durability of the sheet metal rocker arm, the rigidity of even a part in which a stress with the greatest magnitude is generated is secured so that the rigidity of this part does not exceed the allowed value. In such a case, however, a rigidity in other parts becomes excessive. The excessive rigidity hinders reduction of the size and the weight of the sheet metal rocker arm and is not preferable.
The sheet metal rocker arm of the present invention has been contrived considering the above-mentioned circumstances.
The sheet metal rocker arm of the present invention is manufactured by subjecting one metal plate to punching and bending. The sheet metal rocker arm is provided with a pair of side walls which are substantially parallel to each other, a connecting portion for connecting the respective end edges of both of the side walls in the width direction, a pair of through holes formed at positions aligned with each other on the side walls, a first engagement portion provided in a part of the connecting portion to abut upon the base end portion of a valve unit, and a second engagement portion provided in another part of this connecting portion to abut upon the leading end portion of a rush adjuster.
Specially, in the sheet metal rocker arm of the present invention, the thickness of the first engagement portion is formed to be greater than that of the side wall. Both of the side walls in a state that they stand up from the connecting portion, are not formed over the entire edge portions of the both sides of these first and second engagement portions. The forms and the sizes of the respective parts are restricted so that a ratio of the maximum value to the minimum value of the stress generated in the first and second engagement portion is within five, based on the load applied to the first and second engagement portions from the valve unit and the rush adjuster.
According to the sheet metal rocker arm of the present invention having such structure as described above, though the rocker arm is formed of one metal plate having the uniform thickness in a unitary integral structure, the thickness of the connecting portion for constituting the first engagement portion is formed to be greater than that of the paired side walls. Accordingly, it is possible to secure the strength and the rigidity of the sheet metal rocker arm by decreasing a stress acting on the first engagement portion, without unnecessarily increasing the weight of the rocker arm. It is suffice if the thickness of the side walls is enough to maintain the strength and the rigidity required for these side walls and is not required to be unnecessarily great. Consequently, it is possible to reduce the width of the sheet metal rocker arm, which is a distance between the outer side surfaces of the side walls so that it becomes easier to incorporate this rocker arm within a limited space inside the engine.
Moreover, since the whole sheet metal rocker arm is formed of one metal plate in a unitary integral structure, a trouble for connecting the plural constituent members that are separately manufactured to each other, is eliminated, which results in the reduced number of processing steps to prevent an increase of the manufacturing cost and deterioration in accuracy. It is also possible to manufacture the sheet metal rocker arm with a high quality at a low cost without providing unnecessary complicated equipment for the assembly and positioning.
Out of the side walls to which a great stress is not applied when the rocker arm is in use, the both side edge portions of the first and second engagement portions are partially omitted except a part required for supporting the pivot for supporting the roller. Further, since the forms and the sizes of the respective parts are restricted in such a manner that a ratio of the maximum value to the minimum value of a stress generated in these first and second engagement portions is within five, there is no part having an excessive rigidity. Thus, the effect of reducing the weight of the sheet metal rocker arm as a whole becomes more excellent.
A cam follower which is provided with the sheet metal rocker arm of the present invention and an assembling method thereof have been contrived to solve problems as described above.
Out of the cam follower provided with the sheet metal rocker arm of the present invention and the assembling method thereof, the cam follower provided with a sheet metal rocker arm comprises a sheet metal rocker arm provided with a pair of side walls which are formed of a metal plate to be substantially parallel to each other and a connecting portion for connecting these side walls to each other, a pivot which is fixed to bridge over the paired side walls by caulking the both ends thereof toward the inner peripheral surfaces of a pair of through holes in a state that the pivot bridges over the paired through holes formed at positions aligned with each other on the side walls, and a roller supported rotatably around a middle part of this pivot.
Specially, in the cam follower provided with the sheet metal rocker arm of the present invention, it is preferable to make the paired side walls to be parallel to each other in a state that the both ends of this pivot are caulked, by forming a gap between the portions at which the through holes are formed, out of the paired side walls, in a state prior to that the both ends of the pivot are caulked, to be wider than this gap in a state that the both ends of the pivot have been caulked.
Specially, in the assembling method of the cam follower which is provided with the sheet metal rocker arm of the present invention, a gap between the portions at which the through holes are formed, out of the pair of side walls, in a state prior to the caulking the both ends of the pivot, is formed to be wider than this gap in a state that the both ends of this pivot have been caulked. Then, it is preferable to form the paired side walls to be parallel to each other by reducing the gap between the portions at which the through holes are formed on the paired side walls, upon the caulking of the both ends of this pivot.
According to the cam follower provided with the sheet metal rocker arm of the present invention having the structure as mentioned above and the assembling method thereof, in a state that the sheet metal rocker arm, the roller, and the pivot are combined with each other and the both ends of this pivot are connected and fixed to the paired side walls for constituting this sheet metal rocker arm, both of these side walls and the both end surfaces of the roller in the axial direction can be formed to be parallel to each other. Consequently, it is possible to sufficiently form between the inner side surfaces of the side walls and the both end surfaces of the roller in the axial direction an oil film for reducing a friction between these surfaces, thereby reducing a resistance required for rotating the roller and reducing an amount of abrasion of the roller and the sheet metal rocker arm.
The cam follower provided with the sheet metal rocker arm of the present invention has been contrived considering these circumstances to reduce a frictional resistance in a contact portion between the end surfaces of the roller in the axial direction and the inner side surfaces of the side walls.
Any cam follower provided with the sheet metal rocker arm of the present invention comprises a pair of side walls which are formed of a metal plate to be parallel to each other, a sheet metal rocker arm provided with a connecting portion for connecting these side walls; a pivot fixed to bridge over the paired side walls by supporting the both end portions thereof at a pair of through holes formed a positions aligned with each other on the both side walls, and a roller supported rotatably around a middle part of this pivot.
In the cam follower provided with the sheet metal rocker arm, a recess for receiving lubricating oil is preferably formed on the inner side surface of at least one side walls out of the paired side walls in such a manner that one end thereof is open at the outer edge of said side wall and the recess is inclined in a direction which becomes shallower toward the opposite end.
In the cam follower provided with the sheet metal rocker arm, the degree of flatness of the inner side surface of each of the side walls is preferably not more than 10 ▪m, and the surface roughness thereof not more than 0.3▪mRa.
Also, in the cam follower provided with the sheet metal rocker arm, it is preferable to conduct a solid lubricating film coating or soft nitriding at least on the inner side surface of the side walls to reduce a frictional coefficient of this inner side surface.
Further, in the cam follower provided with the sheet metal rocker arm, it is preferable to provide washers rotatably around the pivot between the inner side surfaces of the side walls and the both end surfaces of the roller in the axial direction or the both end surfaces of a needle for constituting a radial needle bearing provided on the inner diameter side of this roller.
According to any cam follower provided with the sheet metal rocker arm of the present invention having a structure as mentioned above, it is possible to reduce a frictional resistance between the end surfaces of the roller in the axial direction and the inner side surface of the side walls to reduce a rotational resistance of this roller, and to reduce abrasion of this roller and the sheet metal rocker arm.